Technical Field
The present disclosure relates to illumination devices, and more particularly relates to an LED tube lamp with a detection circuit for detecting whether the LED tube lamp is being supplied by an incompatible ballast or for regulating the continuity of current to flow through its LED unit(s) used to emit light, or a protection circuit for providing overvoltage and/or overcurrent protection.
Related Art
LED (light emitting diode) lighting technology is rapidly developing to replace traditional incandescent and fluorescent lightings. LED tube lamps are mercury-free in comparison with fluorescent tube lamps that need to be filled with inert gas and mercury. Thus, it is not surprising that LED tube lamps are becoming a highly desired illumination option among different available lighting systems used in homes and workplaces, which used to be dominated by traditional lighting options such as compact fluorescent light bulbs (CFLs) and fluorescent tube lamps. Benefits of LED tube lamps include improved durability and longevity and far less energy consumption; therefore, when taking into account all factors, they would typically be considered as a cost effective lighting option.
Typical LED tube lamps have a lamp tube, a circuit board disposed inside the lamp tube with light sources being mounted on the circuit board, and end caps accompanying a power supply provided at two ends of the lamp tube with the electricity from the power supply transmitted to the light sources through the circuit board. However, existing LED tube lamps have certain drawbacks.
First, the typical circuit board is rigid and allows the entire lamp tube to maintain a straight tube configuration when the lamp tube is partially ruptured or broken, and this gives the user a false impression that the LED tube lamp remains usable and is likely to cause the user to be electrically shocked upon handling or installation of the LED tube lamp.
Second, the rigid circuit board is typically electrically connected with the end caps by way of wire bonding, in which the wires may be easily damaged and even broken due to any move during manufacturing, transportation, and usage of the LED tube lamp and therefore may disable the LED tube lamp.
Further, circuit design of current LED tube lamps mostly doesn't provide suitable solutions for complying with relevant certification standards and for better compatibility with the driving structure using a ballast originally for a fluorescent lamp. For example, since there are usually no electronic components in a fluorescent lamp, it's fairly easy for a fluorescent lamp to be certified under EMI (electromagnetic interference) standards and safety standards for lighting equipment as provided by Underwriters Laboratories (UL). However, there are a considerable number of electronic components in an LED tube lamp, and therefore consideration of the impacts caused by the layout (structure) of the electronic components is important, resulting in difficulties in complying with such standards.
Common main types of electrical ballast include instant-start ballast and programmed-start ballast. Electrical ballast typically includes a resonant circuit and is designed to match the loading characteristics of a fluorescent lamp in driving the fluorescent lamp. For example, for properly starting a fluorescent lamp, the ballast provides driving methods respectively corresponding to the fluorescent lamp working as a capacitive device before emitting light, and working as a resistive device upon emitting light. But an LED is a nonlinear component with significantly different characteristics from a fluorescent lamp. Therefore, using an LED tube lamp with a ballast impacts the resonant circuit design of the ballast, which may cause a compatibility problem. Generally, a programmed-start ballast will detect the presence of a filament in a fluorescent lamp, but traditional LED driving circuits cannot support the detection and may cause a failure of the filament detection and thus failure of the starting of the LED tube lamp.
Further, a ballast is in effect a current source, and when it acts as a power supply of an LED tube lamp, problems of overvoltage and overcurrent or undervoltage and undercurrent are likely to occur, resulting in damaging of electronic components in the LED tube lamp or unstable provision of lighting by the LED tube lamp. An instance of such problems may happen when using some models of electronic ballast to supply an LED tube lamp. When such a ballast model is working normally, the ballast provides a high frequency current conforming to its design requirement to the LED tube lamp. When such a ballast model is incompatible or (suddenly) operating abnormally, however, the current output by the ballast may be (instantaneously) increased such that an overcurrent condition happens in the LED module or unit (comprising LEDs) of the LED tube lamp, to cause burning or breaking of the light strip (or circuit sheet) of the LED tube lamp on which the LEDs are disposed. Since an electronic ballast is typically designed to output a constant current and a relatively high voltage, in serious overcurrent/overvoltage conditions the gap or break caused in the light strip may produce an electric arc and high temperature, which may even burn and break the lamp tube and the plastic cover of the LED tube lamp.
Further, the driving of an LED uses a DC driving signal, but the driving signal for a fluorescent lamp is a low-frequency, low-voltage AC signal as provided by an AC powerline or an inductive ballast, a high-frequency, high-voltage AC signal provided by an electronic ballast, or even a DC signal provided by a battery for emergency lighting applications. Since the voltages and frequency spectrums of these types of signals differ significantly, simply performing a rectification to produce the required DC driving signal in an LED tube lamp is typically not competent at achieving the LED tube lamp's compatibility with traditional driving systems of a fluorescent lamp.
Conventional fluorescent lamps and LED lamps are typically not equipped with advanced abilities both to regulate their electrical currents for better qualities or functions and to be compatible with various types of ballasts avoiding typical needs to find a suitable lamp when the fluorescent or LED lamp is not compatible with a present type of ballast.
Accordingly, the present disclosure and its embodiments are herein provided.